New dump functions support

• Added support for Symfony VarDumper (#16)
• Added support for Laravel dd function (#20)
• Added support for Doctrine dump (#22)
• Added support for Tracy (#27)
• Dropped support for PHP 5.3 and for HHVM
• Automatic testing for PHP 7.1-7.2
• Converted to PSR-4 standard

v0.2

Released version 0.2